Neutron reactions and nuclear cosmo-chronology

The beta-decay of Re-187 (t(1/2) = 42.3 Gyr) represents a suited cosmo-chronometer for the age of the r-process abundances, since the radiogenic part of the daughter isotope (OS)-O-187 is defined by the difference between the solar Os-187 abundance and s-process contribution to Os-187. The latter component can be determined via the s-process systematics based on the stellar neutron capture cross sections of Os-186 and Os-187. The laboratory cross section of Os-187 requires a significant correction for the effect of the low-lying excited state at 9.75 keV, which is strongly populated under stellar conditions. This theoretical correction can be improved by an experimental cross section for inelastic scattering to the 9.75 keV state. High resolution time-of-flight measurements of (n, gamma) cross sections of (OS)-O-186,187,188 from I eV to I MeV at CERN n-TOF facility are reported. The inferred stellar cross sections differ from previously recommended values. In addition, the inelastic scattering cross section has been measured at 30 keV neutron energy via time-of-flight at the Karlsruhe 3.7 MV Van de Graaff. The implications of these results for the Re/Os clock are discussed. (c) 2007 Elsevier B.V. All rights reserved. ispartof: Progress in Particle and Nuclear Physics vol:59 issue:1 pages:165-173 ispartof: location:ITALY, Erice status: published